1. Field of the Invention
The present invention relates to a photovoltaic and fuel cell hybrid generation system (hereinafter “PV-FC hybrid generation system”), and a method of controlling the same, and more particularly, to a PV-FC hybrid generation system using a single converter and a single inverter, which achieves a reduction in the number of costly converters and inverters required, and a method of controlling the same.
2. Description of the Related Art
Since the late 20th century, the demand for developing renewable energy sources has increased due to the depletion of fossil fuels, and the environmental pollution and global warming associated with CO2, NOx and SOx emissions. Notably, the demand for renewable energy technology has recently increased sharply due to soaring international oil prices and greenhouse gas reductions obligated by the Kyoto protocol. Thus, matters regarding current energy resources are linked directly to national security, and the volition and technology to reduce CO2 emissions are considered to significantly affect a nation's competitiveness.
Among a variety of renewable energy sources, solar cells (i.e., photovoltaic cells: PV), despite low efficiency, are expanding their domestic market share due to their features as clean energy and their advantages conforming with Korean domestic semiconductor technologies. In overseas markets, the commercialization of photovoltaic generation systems, led by Japan and German, has been completed based on those countries' long-term accumulated technical skills and financial abilities.
However, photovoltaic cells have the following limitations: generating power only in the daytime, working as intermittent generation sources dependent upon environmental conditions such as cloud cover and rain, and having the very low maximum efficiency of approximately 10% to 15%. For this reason, photovoltaic cells for home use are utilized only during the daytime, and the commercial power grid supplies power at night and under environmental limitations.
To prevent the above limitations, hybrid generation systems, such as PV-Battery, PV-Wind, PV-Diesel or PV-FC hybrid systems, are under development mainly in the world's leading technological nations. It is therefore currently considered important for nations to take the lead in hybrid power generation system technologies and markets.
However, PV-Battery hybrid systems are disadvantageous in that a battery is not a power generation device, but rather a secondary cell having a short useful lifespan that causes pollution during the manufacturing and discarding process.
PV-Wind hybrid systems also have disadvantages in that a wind power generation source is an intermittent power generation source that is dependent upon environmental conditions, and is not suitable for home use due to its restrictions in terms of installation space and noise. As for PV-Diesel hybrid systems, a fossil fuel needs to be used and this places a limit on its development into an ultimate future power generation system.
A PV-FC hybrid system is considered to be the most competitive generation system as a future hybrid generation source due to the following reasons: this hybrid generation system uses hydrogen and oxygen as fuel, both of which are infinite clean energy sources, conforming with the hydrogen economy society at which the government is aiming, has sufficiently high generation efficiency (35% to 80% in Combined Heat and Power (CHP)), and utilizes a fuel cell that is capable of constant power generation. In the PV-FC hybrid system, a fuel cell constantly generates power so as to maintain a basic load, and PV power is supplied to the grid during the daytime. Thereafter, water is subjected to electrolysis using surplus PV power to thereby generate hydrogen, and the generated hydrogen is used as the fuel of the fuel cell. Consequently, the PV-FC hybrid system can advantageously serve as ultimate eco-friendly infinite energy sources.
However, due to the different output characteristics of the photovoltaic and fuel cells, the PV-FC hybrid system has a 2CON-2INV structure including two converters and two inverters, namely, PV and FC converters and PV and FC inverters. This results in increases in manufacturing cost and size, obstructing the realization of a practical hybrid generation system.